The present invention is directed to a diaphragm-clamping device which is particularly useful in clamping the periphery of a diaphragm-type piston between adjoining plate members, such as the plate members employed in laminated valve assemblies.
Present practice utilizes a diaphragm clamping bead (a) that is formed in a groove (b) in the face of at least one plate member (c), as represented in FIG. 1 of the drawing. The crest of this bead (a) is dimensioned to be slightly below the face of plate member (c) to permit simple machining of the plate surface without interference with the clamping bead. Tight machining tolerances are required on this clamping bead. Typically, the thickness of diaphragm (d) is on the order of 0.060 inch, which has been found to provide both flexibility and strength within acceptable standards. With a standard-type gasket (e) between the adjoining plate members (c, f), the periphery (g) of the diaphragm (d) is compressed between the clamping bead (a) of plate member (c) and the face of the adjoining plate member (f) to 0.030.+-.0.002 inch. It will be appreciated, therefore, that the diaphragm (d) is reduced to approximately one-half its original thickness at the point of clamping. This pinching of the gasket between the clamping bead (a) and adjoining plate (c) is sufficient to normally prevent the periphery of diaphragm (d) from being pulled out of its clamped position between the adjoining plate members. In addition, the periphery of diaphragm (d) is normally formed with an enlarged end (h), so that, even if the diaphragm (d) should take a set, so as to lose its tension where it is clamped in position, the enlarged end of the diaphragm is prevented from being pulled through the reduced area between the clamping bead (a) and the adjoining plate member (c).
In certain applications, however, a new, high-pressure gasket is required, such as that disclosed in U.S. patent application Ser. No. 375,908, filed May 7, 1982, and assigned to the assignee of the present invention. This high-pressure gasket is relatively thick prior to compression and, following sufficient compression to achieve the desired high unit load sealing forces, measures approximately 0.060 inch in thickness. Thus, the distance between the clamping bead and adjoining plate member, when using such a high-pressure sealing gasket, is increased such as to preclude obtaining a sufficient clamping force on a standard-type diaphragm. This problem could be overcome by increasing the height of the clamping bead, but this solution would raise the crest of the clamping bead above the face of the plate member and, therefore, interfere with machining operations on the face of the plate member having the clamping bead.